1. Field of the Invention
This invention relates generally to the fabrication of storage and dispensing systems for the selective dispensing of fluids from a vessel or storage container in which the fluid component(s) are held in sorptive relationship to a solid sorbent medium, and are desorptively released from the sorbent medium in the dispensing operation.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluid(s).
Such process and application areas include semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical intervention and therapy, water treatment, emergency breathing equipment, welding operations, space-based delivery of liquids and gases, etc.
U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus, describes a gas storage and dispensing system, for the storage and dispensing of gases. The gas storage and dispensing system of the Tom et al. patent comprises an adsorption-desorption apparatus, for storage and dispensing of gases, e.g., hydride gases, halide gases, organometallic Group V compounds, etc., including: a storage and dispensing vessel constructed and arranged for holding a solid-phase physical sorbent medium, and for selectively flowing gas into and out of said vessel; a solid-phase physical sorbent medium disposed in said storage and dispensing vessel at an interior gas pressure; a sorbate gas physically adsorbed on the solid-phase physical sorbent medium; and a dispensing assembly coupled in gas flow communication with the storage and dispensing vessel, for selectively discharging gas from the vessel with desorption of the gas from the sorbent medium in the vessel.
The desorption may be effected by thermally desorbing the gas to be dispensed, or by providing a pressure differential between the vessel interior volume and an exterior dispensing locus, e.g., by imposition of a vacuum on the storage and dispensing vessel or by pumping the gas to the desired site of use of the dispensed gas. As a result of such dispensing modes, the gas pressure in the storage and dispensing vessel may be at atmospheric or below atmospheric pressure levels.
The storage and dispensing vessel of the Tom et al. patent thus embodies a substantial advance in the art, relative to the prior art use of high pressure gas cylinders. Conventional high pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture if internal decomposition of the gas leads to rapid increasing interior gas pressure in the cylinder and the risk of cylinder rupture or other unwanted bulk release of gas from the cylinder.
The gas storage and dispensing vessel of the Tom et al. patent reduces the pressure of stored sorbate gases by reversibly adsorbing them onto a carrier sorbent medium, e.g., a zeolite or activated carbon material.
In use of the gas storage and dispensing system of the above-described Tom et al. patent, it is desirable to dispense storage gas at a high level of purity in a number of end use applications, such as for example in the manufacture of microelectronic device structures.
In many instances, this desired high purity characteristic of the gas storage and dispensing system is compromised by the residual or "native" contaminants sorptively retained on the sorbent material. This is attributable to the sorptive character of such materials, and is characteristic of all commercially available sorbent materials to some degree, with the extent or concentration of such extraneous sorbable species varying depending on the specific sorbent composition, its manufacturing process, and its history of storage, transport and environmental exposure.
Thus, for example, a sorbent material which is manufactured with high degree of purity may nonetheless in subsequent storage be exposed to atmospheric moisture and ambient gases, or to gas species in the containers in which such sorbent materials are originally furnished from the manufacturer, which sorb on and contaminate the sorbent material.
Under such circumstances, when the sorbent material containing extraneous sorbable species is loaded in the gas storage and dispensing vessel, and the dispensing gas (i.e., the gas to be stored and thereafter selectively dispensed from the vessel) is introduced to the sorbent for take-up and loading thereon, the sorptive capacity of the sorbent material may be adversely affected by the presence of the extraneous sorbables. Additionally, such extraneous sorbables then can desorb during the subsequent dispensing operation, with the result that the dispensed gas is of reduced purity due to the extraneous sorbables therein.
For example, when an activated carbon sorbent material is employed in the gas storage and dispensing vessel and the vessel holding the sorbent is loaded with a hydride gas such as arsine (e.g., for subsequent dispensing in ion implantation operations to produce arsenic-doped semiconductor substrates), the dispensed arsine gas may contain relatively high carbon monoxide and carbon dioxide impurity levels deriving from the originally provided activated carbon sorbent--carbon monoxide levels which are as high as 20-50 parts per million by volume (ppmv) or higher, and corresponding carbon dioxide levels which may exceed 100 ppmv.
It would therefore be a significant advance in the art of such gas storage and dispensing systems to provide a system which overcomes such extraneous sorbables impurity problem, and enables the on-demand dispensing of high-impurity gas.
It therefore is an object of the invention to provide a gas storage and dispensing system of the general type disclosed in Tom et al. U.S. Pat. No. 5,518,528 which obviates such extraneous sorbables problem and enables selective dispensing of high purity gas.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.